Zirconium steel and process of making same



was Sept. 2, 192,4.

UNITED-STATES PA E T OFFICE. I

:nmonmcx I. Backer, on NEW .YORK, N. Y., ASSIGNOB 'ro ELECTED METALLURGI- cs1: 'comemx, on NEW YORK, 1y. Y., A CORPORATION or WEST VIRGINIA.

. zmcomuu srnnr. ann'raocnssor MAKING sum.

Io Drawing.-

To all whom, a m mom:

Be it known that I, FREDERICK M. BEOKET,

high-sulphur content, said steel being nevertheless free from the so-called red-short ness which has heretofore been considered as a necessar characteristic-of all such highsulphur stee s. Theseresults are attained,

in accordance with the present invention, by

the addition of zirconium to the molten steel,

optimum treating conditions being hereinafter set forth.

As is well known, the deleterious effects of a high-sulphur content in steel are most apparent during rolling or forging at the" customary high temperatures re uired by these operations. The term red-s ortness applies tothe'tearing or cracking of the steel during such hot-working'operations. The occurrenceof red-shortness in a steel may in aggravated cases cause the inetal to bre up completely under the rolls or ham-. mer, just as though were-possessed the rolled or forged steel" shows upon inspection of its.surface,'cracks, fissures, or reticulated systems of seams, which in themselves are suflicient to causethe' rejection of the material. High-sulphur steels exhibiting the less severe type of red-shortness may in numerous instances'fail to show upon comparison with low-sulphur steels, an'yf-ap preclabl'e decrease in t e' values 'ofgthose' commonly determined mechanical pfoper 'ties,such as tensile strength, percentage elongation, Izod number, etc.', which are referred to measurements made in the cold; and especially is this true if the test-pieces great brittleness; while in less severe cases ,with his own revious ezlperience with that I from the high-sulphur steel are taken at ap ease. mea au' ust 11, 1922. serial 110. 581,285. 1

some distance from the surface of the rolled or forged metal so as to escape the major surface cracks or seams.

In consequence of the above-mentioned facts, it follows that the most reliable test 5 of the efiicacy-of any given addition agent in counteracting the harmful effect of sulphur consists in an examination into the actual behavior of the etc 1 under rolling on forging operations, and it as been by means", so of such experimental work that the bene fical effect of zirconium upon high-sulphur steel which forms the basis of the resent invention has been most conclusively emonstrated.'

In those cases amon existingA. S. T. M. specifications for stee where a maximum rails, splice bars, track bolts and spikes,

structural steel forbuildings, and concrete reinforcement bars, it is true that no limits for sulphufare specified. But in practice there are always allowable limits of sulphur assigned for any given steel, which limits are either the result of an agreement between manufacturer and purchaser or are voluntarily set by the manufacturer in accordance particular gra e of steel.

It is therefore not racticable for the urposes' of the present invention arbitrar' y to define what'is meant by the term h1 ghsulphur steel. Not onl does the maximum sulphur limit vary wit the grade of 'steel produced and especially with the'manganese content of the same, but this maximum prac-' tical limit depends largely upon the exact manner in which the metal is rolled or forged. I

I regard as being within the scope of m invention the treatment of any steel wit zirconium' which results in an unmistakable improvement in those hot-working properties which are dependent upon the sulphur content, as well as the product thereby produced. In many cases, such application of zirconium makes possible the satisfactory rolling or forging of steel which could not otherwise be worked owing to its high-sulphur content.

The use of zirconium as a deoxidizer, solidifier, and scavenger of steel, as has'often been proposed, as well as its use to counteract the embrittling' effect of phosporus (cold-shortness) in high-phosphorus steels, as set forth in a coending application of F. M. Becket, erial No. 528,283, filed January 10, 1922, are to be clearly distinguished from that described herein, which contemplates the employment of this metal for the specific purpose of improving its hot-working properties.

In the course of this investigation it has been found that the beneficial effect of zirconium upon the hot-working properties of high-sulphur steels is in some Way correlated with the fact, which we have observed, that in many if not indeed in all cases zirconium enters into chemical combination with sulphur in the steel melt. While this zirconium-sulphur compound has .not yet been isolated or definitely identified microscopically, its existence is demonstrated by the effect of zirconium upon the amount of hydrogen sulphide evolved when the steel is treated with 1:1 hydrochloric acid in accordance with the usual evolution-titration method of analysis. From the results of numerous analyses made on steels of different sulphur contents and treated with different amounts of zirconium, it has been established (a) that an acid-insoluble zirconium sulphide or zirconium-sulphur combination is formed; and (b) that only the zirconium in excess of a definite quantity which appears to bev of the order of 0.10--0.15% added zirconium takes part in this sulfid-forming under the conditions employed in this investigation approximately 0.100.15% added zirconium was used up in the course of other chemical reactions, probably involving1 the oxygen and nitrogen present in the me t.

- The percentage of zirconium which must be added to the molten steel to obtain the maximum beneficial effects is determined by a multiplicity of factors, includin .tempera-' ture and degree of oxidation 0 the steel bath; the composition of the steel; the composition of the alloy or aggregate containing zirconium which is used; the manner in which the/addition is made; and the ty e and severity of hot-working to which tlie steel is subjected before it is put into use in: finished form. For example, in the manu faoture of carbon steels containing around however, involvin reaction. In other words Our experiments have shown that the above-described beneficial effect ofzirconium is primarily due, not to the actual elimination of sulphur from the steel bath, but to the fixation of the sulphur by means of chemical combination with zirconium. As has been stated, a zirconium-sulphur compound which is insoluble in 1:1 hydrochloric acid may be produced, so that an ordinary analy: sis of the treated steel for sulphur by means of the evolution-titration method might lead one to conclude that sul hur was actually eliminated. in amount indlcated by the equation cited above. Gravimetric analysis,

solution in and oxidation by nitric aci followed by precipitaton as barium sulphate, discloses the fact that this apparent quantitative elimination of sulphur is due to the formation of a compound insoluble in 1:1 hydrochloric acid. Further investigation on this point has revealed the fact that in addition to this quantitativeelimination of sulphur, which is only apparent, there may be and very often is an actual elimination of sulphur fromthe bath which in its extent depends upon a multiplicity of factors, chief among which is the length of time the steel is held in the furnace or ladle subsequent to the addition of zirconium. This time element is associated with those progressive processes which result in the separation of lighter, non-metallic particles and globules from a fluid metal bath,-processes which are well-understood by those familiar with the art.

Whereas, therefore, actual slaggin off and elimination of the zirconium-Sn phur ompound depends upon the formation of said compound, this subsequent rocess of elimination of sulphur must not e regarded as an essential feature of the present invention, although it is'a feature which is advantageous and should be encouraged in practice.

The investigation into the treatment of high-sulphur steels with zirconium has included the making of a number of heats of steel; the casting of ingots; the rolling and forging of ingots; and the machining and testing of various test-pieces. Equal weights of molten steel were tapped from the furnace into two separate ladles in the case of each heat. The A ladle was in each case treated with silicon-zirconium and the 13" ladle with 50% ferrosilicon, each of the two additions being adjusted to correspond to the same amount of added silicon. The ladles of steel after treatment were teemed into, tapered molds of the usual type and the two Silicon-zirconium.

Per cent. Zirconium --44.53 Silicon ..50."?? Iron 2.54 Titanium 0.70 Carbon 0.48

Since the efiect of zirconium which is herein described consists in an improvement of hot-working properties and eliminasoil of red-shortness, it is not feasible to present the results of the investigation in the form of tables or curves. For pu oses of illustration, however, an account 0 the results obtained in the case of a typical heat will be 'ven.

This eat of steel was poured into two ladles, one ladle (A) bemg treated with 0.15% zirconium and 0.18% silicon as silicon-zirconium and the other ladle (B) with 0.18% silicon only, as ferros'ilicon. The steel had the following analysis:

C Si Mn P S 0.44 0.15 0.28 0.018 0.075

' were rolled directly down to l" plate, without cross-rolling,,1n a commercial mill.

' The temperature of the heating furnace was steel to be entirel maintained at 2010 F. The ingots were rolled to i" plate in about 6 passes at a reduction from 331} to 100% greater .tlianthat normally used, in order to emphasize any red-shortness resent.

Inspection 0 showed the A or silicon-zirconium treated free from cracks, seams, or other impe ections. The :13 plate, treated with the same amount of silicon but without zirconium, was badly broken up and splintered-along the edges over the u per half (corresponding to the {top of t e original ingot) and :contained several bad 'fissures along the edge of the lower half.

The above is one typical experiment selected from a number of similar experiments, in all of which the beneficial efiect of zirconium was unmistakable.

The above-described process will, it is believed, greatly increase the quantity of coking coaavailable for the production of blast-furnace coke, and also make available for steel production a large tonnage of pigthe finished steel plate iron and scrap which is now considered oi-grade because its sulphur content is above the limit set by. specifications. The sul hur problem is one of the most serious which the industry faces toda because of the fact that the open-hearth rnace process, which uses large percentages of scrap steel in its charge, is fi hting a losing fight against the natural ten ency toward the accumulation of scrap higher and higher in its sulphur content. This is due to several difierent factors, as follows: (1) the use 4 of lower-grade coke both in blast-furnaces and in foundries; 2) the difliculty of eliminating suflicient s phur in the open-hearth furnace and particularly in the acid open hearth furnace to make up for the sulphur contained in the fuel which heats the'furnace, and (3) the-tbflcentration of sul hur in the steel bath due to oxidation 0 the steel during the melting-down stage.

Since the use of zirconium will do much toward alleviatin this situation, the practical benefits of e resent invention will be obvio'us to those amiliar with the art.

I claim:

1. Process of treating steels containing suflicient sulphur to cause red-shortness, I

comprising adding zirconium thereto in proportion sufiicient to counteract to a substantial degree the detrimental effect of the sulphur.

2. Process of treating steels containing sufiicient sul hur to cause red-shortness, comprising ding zirconuim thereto in the proportion of about 0.15 to 0.50% zirconium, calculated on the weight of the steel.

3. Process of treatmg steels containing not less than 0.05% sulphur which comprises adding zirconium thereto in proportion sufiicient to counteract to a substantial degree the detrimental effect of the sulphur.

4. As a new composition of matter, a high sulphur-steel containing zirconium.

Q 5. As a new composition of matter, steel containing zirconium and upward of 0.05%

sulphur.

6. As a new composition of matter, steel tive freedom from red-shortness as compared with a steel of like composition free from zirconium.

In testimony whereof, I aflix my signature.

FREDERICK BECKET. 

